Wireless communications is currently enjoying a period of rapid technological advancement and tremendous growth in popularity. In order to allow wireless communication to become truly convenient and omnipresent, standards have been developed and implemented so that the various wireless-enabled devices may readily communicate with one another. One such standard has been developed by Bluetooth SIG, Inc. (SIG=“Special Interest Group”), a consortium of companies interested in seeing the growth in wireless networks continue. The standard developed by this group has become known as Bluetooth and devices conforming to the standard are known as Bluetooth devices or Bluetooth-enabled devices. The Bluetooth standard is based on the IEEE (“Institute of Electrical and Electronics Engineers”) 802.11b standard and applies to a short-range radio system designed to replace cables in a personal area network (in the 10 m range). These devices operate in what is known as the Industrial Science and Medicine (“ISM”) communications band around a frequency of 2.45 Ghz. The ISM band actually extends from 2.4 Ghz to 2.480 Ghz and includes 79 communication channels or sub-ranges of frequency, on which devices may communicate.
Many other types of devices operating according to applicable standards also operate on the various channels within the ISM band. For instance, Wireless Local Area Network (“WLAN”) devices (also based on the IEEE 802.11b standard) operate in the ISM. Devices operating according to the WLAN standard are designed to replace a wired LAN infrastructure. Other types of devices that operate in the ISM band include microwaves, various types of monitoring devices such as baby monitors, etc.
Very recently, the IEEE Standards Board adopted a new communications standard, IEEE 802.15.1, known as “Wireless MAC and PHY Specifications for Wireless Personal Area Networks (WPANs™)”. This standard closely mirrors the Bluetooth standard. Adoption of such a standard by the widely-recognized IEEE Standards Board means that wireless devices designed to operate in wireless personal area networks are even more likely to model their operation on this standard. Unless otherwise noted, where specific features or requirements of the Bluetooth standard and Bluetooth devices are discussed below, those same features or requirements are present in the IEEE 802.15.1 standard.
As enabling technologies advance and as standards are developed and adopted, wireless networks and the communications and other applications running thereon, are expected to become more and more prevalent. This area of technology is expected to experience explosive growth over the next several years. Even before the recent standard adoption by the IEEE, it was forecast that by the year 2004 there will be over 100 million Bluetooth devices in the United States alone and over 400 million worldwide.
One problem associated with all types of wireless communications is that signals being transmitted by different devices at the same frequency can interfere with one another. This can be referred to as co-channel interference when it occurs between devices operating in the same ISM channel. Interference can also occur between devices operating at frequencies which are not the same but which are close to one another. For devices operating in adjacent ISM channels, this can be referred to as adjacent interference. Both types of interference can cause communication packets to be lost, garbled or misinterpreted by the receiving device, hindering the practical speed and accuracy of the wireless communications.
In an attempt to minimize the incidence of serious interference, the Bluetooth standard calls for Bluetooth devices to “hop” on all 79 channels within the ISM band. That is, the devices transmit only a certain amount of data on a channel before moving to another channel to continue transmitting. The standard establishes the criteria for hopping—how much data to transmit on each channel, when to hop and the order in which to hop to each channel. Devices following the standard understand these criteria and are able to establish and maintain communications with one another while hopping from channel to channel. Because of the advantages of hopping from channel to channel while transmitting, it is likely that other, non-Bluetooth devices will implement this strategy for avoiding interference.
The Bluetooth standard calls for re-transmitting packets when data is lost in transmission, typically due to interference. The procedure for re-transmitting increases transmission time and degrades the data rate. In many of the applications to which Bluetooth devices are applied, such as voice transmissions over IP (internet protocol), even the smallest degradation in the data rate is unacceptable because the quality of the signal quickly degrades to an unusable state.
Unlike Bluetooth devices, WLAN devices, and most other devices operating in the ISM band, select one static channel and transmit data only on that channel. Because they are designed to operate over a greater distance than Bluetooth devices, WLAN devices transmit much more powerful signals. Therefore, Bluetooth device signals can experience serious interference problems when hopping to a channel upon which a WLAN device is transmitting, or to an adjacent channel. As Bluetooth and WLAN devices, and other types of devices operating in the ISM band, become more and more popular, the prevalence of this type of interference will increase. The resulting degradation in performance will seriously hinder customer acceptance of this emerging technology.
For these reasons, and others readily identified by those skilled in the art, it would be desirable to develop communications techniques applicable to the Bluetooth (and IEEE 802.15.1) standard, and to the communication protocols of any other wireless devices which hop from channel to channel while transmitting, which will minimize the effects on performance of any interference due to the transmission signals of other devices in the ISM band.